This invention relates to reverse osmosis membrane filter elements and cation devices. The basic element in a reverse osmosis filtration system is the polymeric membrane that under specific differential osmotic pressure condition allows the free passage of water while impeding the passage of salt and other impurities.
In the spiral membrane filter elements of the prior art, two membrane sheets separated by a feed water/brine spacer are backed by a water-carrying sheet of material specifically designed to collect the purified water and drain it toward one edge of the membranes. This composite structure is wound around a piece of duct which serves as a purified water collector. The mesh material spacer provides channels between two layers of membrane through which the incoming feed water flows across the surface of the membranes. This type of filtering element must be housed in a pressure vessel so that the feed introduced to the membrane surface is under sufficient pressure to drive the purified water through the membrane barrier. In a typical home water supply line the water pressure falls between 2.8 and 5.6 kilograms per square centimeters (40-80 psi). Under such conditions, the ratio of purified water produced to brine discarded to drain is 1 over 5. In other words, for each liter of purified water produced there is 5 liters of concentrate or brine discarded to the sewer drain. This means that 95 liters (approximately 25 gallons) of feed must flow across the membrane surface to produce 15.5 liters (approximately 4 gallons) of daily household consumption of purified water. Homeowners, in these times of ecological concerns and diminishing potable water resources, are becoming more and more reluctant to use a reverse osmosis filter equipment that wastes potentially five times the amount of water it purifies.
The prior art spiral-wound reverse osmosis filter elements tend to deteriorate quickly due to salt precipitation on the membrane surface which adheres to the mesh-like spacer material or becomes trapped therein. This results in both abrasion of the membrane surface and plugging of the element further reducing its efficiency or causing complete failure through perforation of the membrane. The narrow feed channel of prior art filter elements necessitate continuous feed flow over the membrane surface to prevent excessive salt buildup. The small volume of feed water held between the membrane layers could not sustain operation without discharge of brine for more than a few minutes.